KARBALA, Iraq (AFP) – A series of attacks in Baghdad and a holy Iraqi city killed 12 people, while five others died in a helicopter crash, as major religious ceremonies came to a close, officials said on Wednesday.

In the deadliest attack, mortars killed seven people and wounded 46 in the Shiite holy city of Karbala, south of Baghdad, as pilgrims gathered late on Tuesday to mark the birthday of the Mahdi, the 12th and last Shiite imam.

"Several mortars landed at 11:00 pm (2000 GMT on Tuesday), killing seven pilgrims and injuring 46, in a neighbourhood located four kilometres (2.3 miles) northwest of the centre of the city," a Karbala police officer said.

"The pilgrims were coming from around the city to participate in the ceremony," the officer said, adding several houses were damaged.

Shiites -- the majority of Iraq's population -- believe the imam will return to Earth on the Day of Judgment.

Tuesday's attack came a day after twin car bombings in Karbala killed 21 people and wounded at least 47 others.

Also near Karbala, an Iraqi air force helicopter crashed early on Wednesday while it was providing surveillance for the ceremonies, killing its five-man crew.

"The five-man crew of the helicopter was killed when it crashed as a result of a sandstorm in Ibrahimiyah, east of Karbala," General Anwar Hanna Amin said.

Defence ministry spokesman Major General Mohammed al-Askari confirmed the crash, saying the helicopter was a Russian-designed Mi-17. The crash is being investigated, he added.

In Baghdad, meanwhile, a bomb inside a restaurant on Wednesday morning in the Shiite neighbourhood of Sadr City in the north of the city killed five people, including one woman.

Thirteen others were wounded in the blast, which occurred at about 9:30 am (0630 GMT), officials from the defence and interior ministries said, speaking on condition of anonymity.

US and Iraqi officials have warned of the dangers of an upsurge in violence as negotiations on forming a new governing coalition have dragged on, more than four months after parliamentary elections.